Some years ago CNN did a poll [cnn.com] of Americans, and found that 64% believe aliens have contacted humans, and about half believe in alien abductions. So some of the 71% mentioned above might well expect humans on Mars in twenty years, but that's not necessarily as a result of human effort.

That said despite 64% of respondents believing that aliens have contacted humans, only 54% believe in intelligent extraterrestrial life. Either the poll's methodology was shoddy, or there are a lot of stupid people out there.